You can roam onto another foreign carriers cell networks, as long as they provide data connections, and get Email and the web. Roaming charges from AT&T will apply, so look at your AT&T plan, and ask them if you can pay for data roaming ahead of going abroad to get you a decent rate.

Also, you can use hotel and other free wi-fi hot spots to get Email and Web, without paying roaming charges - you simply use the free Internet hook-up via the wi-fi.

Note - visual voicemail will probably not work when you're off the AT&T network

Also - leaving you iPhone set to automatically download Email, while you are roaming abroad, could be very very expensive without the AT&T international data roaming plan in place - BE CAREFUL!